Best way to heat a small (3'x3'x4') gro-room. heating pad?

So my grow-room is perfect right under my 400w MH 24/7 during veg, with a steady 76F reading. However, I know once I start flowering and have to have a dark cycle, the temp will plummet to the ambient basement temperature, ~50F.

Will a heating pad (or two), like the ones they sell at Walgreens suffice? They make waterproof ones, so I could put it under the plants. I am not sure how much power these things drain, though.

Are the heating pads specifically for germination anything special?

I'd REALLY prefer not to have to run Kerosene/oil heat, due to CO concerns.

Also, I'd prefer not to have to run a 1500w space heater (that's a lot of energy! I'd want more light if I was burning that much!)

My grow room is split in half already, so I am considering making it 50/50 veg/flower (vegging for 18h instead of 24 because my 1000w HPS is going to make a LOT of heat!) In this case, I think venting would be the main concern (particularly during the 6 hours BOTH the 400w MH and 1000w HPS are on), but I should have that covered with my vortex fan

I think the fact that my basement is cool is much easier to manage than if it were hot. Just wondering if anyone had some experience with heating pads as a room-heater during the night.

Cheers!

add a small camping propane heater.It will add some heat and also the burnoff fumes are nothing but pure co2 which if built up during the night will help when the lights come on

Oh yes, one other thing. I would like my room to be self-sufficient for days at a time. I won't be able to manage a flame-based heater.

get a small oil based heater then .The electric kind use 1500 watts and the oil use like 400 watts but can be on timers